System and method for transmitting opc data via networks, in particular the internet, using an asynchronous data connection

ABSTRACT

OPC data is transmitted via data networks, in particular the Internet. A bi-directional data connection via the Internet in both directions, is enabled even across firewalls and starting from an OPC client, which is not visible as a server on the Internet. To achieve this, a first connection request for establishing a first transmission channel is sent from a first data processing device of an OPC client, via a data connection, to an OPC server of an automation system. The OPC server responds to the request using a second transmission channel. The data connection is thus kept open permanently, allowing data to be sent and received bi-permanently, allowing data to be sent and received bi-directionally, said operations being temporally independent of each other, between the OPC client and the OPC server by at least one data network, in particular, the Internet. To guarantee a temporally unlimited service life of a data connection, dummy data is transmitted, for example, at regular intervals from the OPC server to the OPC client, even if no useful OPC data is present, in order to maintain at least one data connection.

[0001] The invention relates to a system and a method for transmittingOPC data via data networks, in particular the Internet, using anasynchronous data connection.

[0002] OPC (OLE for process control) is understood to mean a standardand manufacturer-independent specification of a software interfacebetween Windows applications and automation systems, in particular forproduction control and automation, which permits the flow of databetween an extremely wide range of systems, applications and deviceswithout problems. OPC therefore represents a connection among processcontrol, statistical production control, process optimization, otherproduction applications, for example applications for carrying outproduction or for the production management, the corresponding real-timedevices and Windows applications. For this purpose, it offers a seriesof OLE or COM-based standard interfaces and further adapted interfaces.

[0003] With the aid of data networks, it is possible to establish a dataconnection to a server from any desired computers, clients, as they areknown, which have access to these data networks. This applies inparticular to the World Wide Web (WWW), which is also called theInternet. The terms Web or Internet server or Web or Internet client,used in the following text, are used to illustrate the membership to thespecific data network comprising the Internet, but in functional termsmake no distinction from the meaning of the terms client and serverwhich are used for all possible data networks. In the following text,the terms OPC client and OPC server will be understand to mean thosecomputers which can additionally process data in the OPC data format. Inthe following text, when only the term client or server is used, this isunderstood to mean an OPC client or OPC server.

[0004] In the Internet, a data connection is established to what isknown as a Web or Internet server. The access to an Internet server iscarried out, for example, with the aid of known Internet browsers, forexample Internet Explorer from Microsoft or Netscape Communicator fromNetscape. When a data connection is being established from a Web orInternet client, as they are known, a request is output to an Internetserver by entering and dispatching what is known as a URL address. Whena data connection is established, the Internet server called answerswith what is known as an HTML page (HTML=Hyper Text Markup Language),also called a Web page. The Web clients, as they are known, communicatewith the Web servers by means of transport protocols. Each dataconnection between Web client and Web server is therefore based on arequest protocol and, as a reaction to this, a response protocol.

[0005] Internet connections permit fast data interchange betweenlocations which are physically widely separated. In conjunction with theOPC technology, it is thus possible for extremely different systems,applications and devices which can be located physically very widelyremoved from one another, to communicate with one another simply andquickly. Until now, however, it has not been possible to connect thefull functional scope of the OPC technology to the Internet, since forthis purpose an asynchronous data transmission method, that is to saytime-independent, bidirectional communication, would be necessary, whichhas hitherto not been possible in the Internet.

[0006] The invention is based on the object of specifying a system and amethod for transmitting OPC data via data networks, in particular theInternet, which permits time-independent, bidirectional transmission ofOPC data even between at least two data processing devices that can becoupled to data networks, in particular the Internet, even behind dataprotection devices, in particular fire walls, even if one of the dataprocessing devices is not visible in the data network, in particular theInternet.

[0007] This object is achieved by a method for transmitting OPC data viadata networks, in particular the Internet, in which a first connectionrequest for establishing at least one first transmission channel is sentfrom an OPC client via a data connection to at least one OPC server, atleast one data connection, in particular a transmission channel, beingpermanently open, which is provided for sending, at any desired time andindependently of the actions of the OPC client, OPC data from at leastone OPC server to the OPC client via at least one data network.

[0008] This object is achieved by a system for transmitting OPC data viadata networks, in particular the Internet, comprising at least one dataprocessing device that can be coupled to a data network and belongs toan OPC client, the first data processing device being provided toestablish at least one data connection in the form of a firsttransmission channel to at least one OPC server, at least one dataconnection, in particular a transmission channel, being permanentlyopen, which is provided for sending, at any desired time andindependently of the actions of the OPC client, OPC data from at leastone OPC server to the OPC client via at least one data network.

[0009] The invention is based on the finding that, with the aid of theInternet, a true “active” data connection to a client that is notvisible in the Internet, in particular an OPC client, is not possible,but only a data connection between any desired client connected to theInternet with any desired server that is visible in the Internet, inparticular an OPC server. This disadvantge is overcome in a surprisinglysimple way in that first of all a first transmission channel from theclient to the server of an automation system is established. For thispurpose, from the client which, after the production of thebidirectional data connections, can serve as a fully adequate operatingand observation system for the automation system, a first connectionrequest is sent to the server of the automation system. The serveranswers this connection request and, in order to keep this dataconnection open permanently, the Internet server, for example even whenthere is no useful data present, in particular useful OPC data,transmits dummy data to the client or sends information to the clientwhich informs the client that a transmission of useful data is stillintended. In this case, dummy data is data which is generated by theserver itself for the purpose of maintaining the data connection and issent to the client.

[0010] In this way, a permanently open data connection is installed, viawhich the server, in particular an OPC server and therefore theautomation system, can at any time and independently of actions of theclient, in particular an OPC client, send data, in particular OPC data,asynchronously to the client and therefore to the O&O system.

[0011] Independently of and in parallel with this, client and server canalso communicate with one another conventionally in the Internet, by theclient in each case directing a new request to the server, which isanswered by the latter with an appropriate response.

[0012] A system of mutually independent data connections is thereforeavailable, by means of which both the client, that is to say the O&Osystem, and also the automation system for itself can communicate withone another. Between client and server or, in other words, betweenoperating and observation system and automation system, in functionalterms a bidirectional data connection is ensured which, in particular,also permits data transmission from the server to the client, since theserver is continuously connected to the client via a transmissionchannel that is permanently open, so that chronologically mutuallyindependent bidirectional data transmission in both directions betweenclient and server is made possible. A data connection of this type isparticularly suitable for the operation and observation of an automationsystem, it being possible for the client to function as an operating andobservation system, which can be activated from any desired computerconnected to the Internet. As opposed to conventional Internet dataconnections, the result is therefore an asynchronous data transmissionmethod which does not require of the client the necessity to be visiblein the Internet or to have installed what is known as a Web server(IIS=Internet Information Server). This makes it possible, from anydesired location in the world, in front of and behind data protectiondevices, in particular firewalls, to establish a bidirectional dataconnection to a server. Since the data connection is activated from theclient, that is to say from the O&O system, it is not necessary for theserver to actively establish a data connection to the client.Furthermore, a change in the configuration of the client is not requiredeither.

[0013] Permanent maintenance of a data connection can be ensured bydummy data being transmitted in order to maintain at least onetransmission channel, even when there is no useful data present.

[0014] A particularly advantageous refinement of the invention ischaracterized in that the dummy data is sent from the server to theclient. In this case, it has proven to be particularly advantageous if,when useful data is not present, dummy data is sent from the server tothe client every 25-35 seconds, in order to keep the data connectionopen.

[0015] A further advantageous refinement of the invention ischaracterized in that in order to maintain a permanent data connection,in particular a transmission channel between server and client, theserver sends the client information which informs the client that atransmission of data is intended.

[0016] A further advantageous refinement of the invention ischaracterized in that in order to maintain a data connection, inparticular a transmission channel, permanently, via which quantitativedata up to a defined size is transmitted from the OPC server to the OPCclient, a requirement for a new connection request is sent from the OPCserver to the OPC client before the defined quantity of data is reached,and then a new connection request for establishing at least one newtransmission channel is sent from the OPC client to the OPC server. Asize of 15-25 MB for the quantities of data to be transmitted via atransmission channel has proven to be very advantageous, since thisimproves the performance and the response times of the system to anextraordinary extent because of the communication via firewallcomputers, and therefore the cost/benefit ratio is most effective.

[0017] A further advantageous refinement of the invention ischaracterized in that a transport protocol, in particular an Internettransport protocol, is provided to control the data transmission. Inthis case, the use of the Hypertext Transport Protocol (HTTP) as thetransport protocol has proven to be particularly advantageous, since itsapplication is extraordinarily simple and the effort for adaptation isvery low.

[0018] A particularly advantageous application of the invention, usingthe existing infrastructures, in particular Internet infrastructures,for a bidirectional data transmission, consists in the method ofoperating and observing an automation system, for example, beingprovided via at least one data network, in particular via the Internet,since as a result, for example, remote diagnoses can be implemented verysimply, as a result of which the analysis of faults which occur andtheir rectification in continuous operation of automation systems, forexample, can be carried out cost-effectively at locations physically farremoved from one another.

[0019] A further advantageous refinement of the invention ischaracterized in that the client does not have to be visible in theInternet, nor have to have installed an Internet Information Server(IIS).

[0020] A connection between the automation and communication technologycan be configured in a simple way in that the operating and observationsystem of the client initiates the provision of at least onetransmission channel as a distributed object, in particular as a DCOMobject, and that the connection to the automation system is establishedvia a DCOM server.

[0021] In the following text, the invention will be described andexplained in more detail using exemplary embodiments illustrated in thefigures, in which:

[0022]FIG. 1 shows a block circuit diagram of an exemplary embodiment ofan automation system with Internet coupling for operation andobservation using OPC technology,

[0023]FIG. 2 shows a schematic, time-based illustration for possibleuseful OPC data communication between OPC client and automation systemvia an OPC server and

[0024]FIG. 3 shows an example of the OPC communication between networkOPC clients and network OPC servers via the Internet.

[0025]FIG. 1 shows an exemplary embodiment of a system for operating andobserving automation systems 5 which, for example, comprise programmablelogic controllers (PLC), numerical controllers (NC) and/or drives. Thesystem has an operating and observation system 1 (O&O client), which iscoupled to a firewall computer 2 via an internal data network 6, forexample an Ethernet. The O&O client 1 is simultaneously also the OPCclient 1 in the example shown. The operating and observation system 1,which is also referred to in brief in the following text as the O&Osystem 1, is assigned a local intranet address, which does not have tobe known in the Internet. The line 9 a is used in FIG. 1 to indicate thefirewall of the firewall computer 2, which surrounds the internalcommunication network 31 (=intranet 31) of the firewall server 2. Theworldwide data communication network, the Internet, is identified by thereference symbol 10. The firewall computer 2 can be coupled to theInternet 10 via a connecting line 7, for example ISDN. The automationsystem 5 can be coupled to the Internet 10 via an Internet server 4,which serves as O&O server 4 for the automation system 5 and which, forexample, has the Internet address dcom server.khe.siemens.de/, via aconnecting line 8 and in each case via a second firewall computer 3. TheO&O server 4 in the example shown is at the same time also the OPCserver 4. The second firewall 9 b surrounds the intranet 32 associatedwith the firewall computer 3. The firewall computer 3 is visible in theInternet 10, for example at the Internet address khe.siemens.de.

[0026] The data connection 6, 7, 8 between the client 1 and the server 4is illustrated in the form of two subchannels in FIG. 1 in order tobetter illustrate and explain the respective transmission direction inthe communication between client 1 and server 4 and vice versa. Thesesubchannels contain a first transmission channel 6 a, 7 a, 8 a, whichsymbolizes the communication direction from the client 1 to the server4, and a second transmission channel 6 b, 7 b, 8 b, which symbolizes thecommunication direction from the server 4 to the client 1. Physically,the two subchannels illustrated are a single transmission channel, thatis to say for an answer from the server 4 to an associated query fromthe client 1 to the server 4, the same physical transmission channel isused.

[0027] In the following text, by using the establishment of a connectionbetween the client 1 and the server 4 as an example, the establishmentof a chronologically mutually independent, bidirectional transmittingand receiving connection between the client 1 and the server 4 via theInternet 10 is to be explained. For this purpose, use is made of anasynchronous method which makes it possible for the server 4 to be ableto send data to the client 1 independently of actions of the client 1,which itself does not need to be visible in the Internet 10, that is tosay does not have its own valid Internet address.

[0028] For this purpose, the client 1 sends a first request via theInternet 10 to the server 4 via the first transmission channel 6 a, 7 a,8 a, whereupon the server 4 reacts with an answer, a response as it isknown, via the second transmission channel 6 b, 7 b, 8 b. In order toavoid any chronological interruption to the response, and therefore anybreakage to the data connection 6, 7, 8, the duration of the response isextended to be “infinitely” long. For this purpose, the system is, forexample, notified that still further data is to be sent. This results ina permanently open data connection 6, 7, 8 via which the server 4, andtherefore the automation system 5, at any time and independently ofactions of the client 1, can send data asynchronously to the client 1and therefore to the O&O system. In order to keep the data connection 6,7, 8 open permanently, it is for example also possible to send dummydata from the server 4 to the client 1 at regular intervals,advantageously every 25-35 seconds.

[0029] Independently of this permanently open data connection 6, 7, 8,“normal” communication can also take place between the client 1 and theserver 4 via the Internet 10, that is to say the client 1 sends arequest to the server 4 via a new transmission channel and the server 4answers this request with an appropriate response via this transmissionchannel. After the data has been transmitted, the new transmissionchannel is closed again. It is thus possible for the client 1 and alsothe server 4 to send and receive data bidirectionally chronologicallyindependently of each other. In order to control the data transmission,a transport protocol, in particular an Internet transport protocol, isused. For this purpose, the Hypertext Transport Protocol (HTTP) isadvantageously used as the transport protocol.

[0030]FIG. 2 shows the chronological sequence of the establishment 26 ofa permanently open data connection 6, 7, 8 between an OPC client 1 andan OPC server 4, to which an automation system 5, designated a PLC(=Programmable Logic Controller) as an example, is connected. Therepresentation is made with the aid of UML notation (Unified ModelingLanguage). Furthermore, FIG. 2 shows the bidirectional communicationwhich, after the data connection has been established, can be initiatedby OPC client 1 and OPC server 4 chronologically independently of eachother. The time sequence for establishing the data connection is asfollows: the OPC client 1 makes a request 11 to the server 4, whichanswers said request with a response 12, this data connection not beingcleared. For this purpose, the OPC client 1 is, for example, informedthat still further data is to be dispatched, as a result of which thisdata connection is kept permanently open. In order to keep the dataconnection open permanently, it is also possible, for example, to senddummy data from the OPC server 4 to the OPC client 1 at regularintervals, in particular every 25-35 seconds, if no useful OPC data canbe sent.

[0031] As a result, the OPC server 4 and the automation system 5 coupledto the OPC server 4 can send data to the OPC client 1 at any desiredtime, independently of the OPC client 1. Following the response 12 ofthe OPC server 4, for example the O&O system 1 places an OPC call, whichis present in the OPC data format, on the automation system 5. To thisend, the OPC client 1 converts the OPC call, which is present in the OPCdata format, into an OPC subscribe in the Internet-compatible dataformat. The OPC client 1 sends the OPC subscriber 13 via a new dataconnection to the OPC server 4. The OPC server 4 converts the OPCsubscribe in the Internet-compatible data format into the original OPCcall in the OPC data format again. This call is passed on to the PLC 5as an OPC request 28. The PLC sends back an OPC response 29 in the OPCdata format to the OPC server 4, which converts the OPC response into anInternet-compatible data format and passes it on as a response 14 to theOPC client 1 (=synchronous behavior). This data connection is closedagain after the data transmission has been carried out. The OPC client 1converts the response in the Internet-compatible data format into theoriginal OPC format again and passes it on to the O&O system 1 forfurther processing.

[0032] Independently of and in parallel with this, the OPC server 4 isable to communicate messages, alarms or else variable changes, forexample, to the OPC client 1 via the permanently open data connection12, as reactions to an event 30 in the PLC 5, without the OPC client 1previously having made a request (=asynchronous OnDataChange or Callback16). The OPC server 4 and the OPC client 1 in each case carry out thenecessary conversions already described into the necessary data formats.This form of communication would not be possible in a “normal” HTTPconnection.

[0033] The asynchronous Callback 16 is in particular alsochronologically possible between a request and a response that has notyet been made.

[0034] The result overall is therefore useful OPC data communication 27via the Internet in both directions, which can be initiated from bothsides and is mutually chronologically independent. It therefore becomespossible to use existing communication paths of the Internet in theusual way even in the region of automation engineering, in particularthe use of the OPC technology, for operating and observation purposes asan HMI interface (Human Machine Interface). One advantageous applicationconsidered is, for example, the operating and observation system WinCCfrom Siemens. The system and method according to the invention permitsthe transmission of DCOM jobs from an OPC client 1 to the OPC server 4.The special feature in this case is that the method permits the OPCserver 4 to send DCOM events to its OPC client 1, without the latterhaving a “true” address, that is to say one visible in the Internet. TheOPC client 1 therefore does not need to be visible in the Internet, nordoes it need to have installed an Internet Information Server (IIS). Onthe client side, no additional costs are therefore required, sinceInternet browsers such as the Internet Explorer from Microsoft or theNetscape Communicator from Netscape are available everywhere. Thus, nospecific special solutions are required for data interchange between theautomation system and O&O user, for example for alarm purposes.

[0035]FIG. 3 shows, by way of example, the OPC communication betweennetwork OPC clients and network OPC servers via the Internet.

[0036] A plurality of OPC clients, of which only one OPC client 20 hasbeen shown for reasons of clarity, are networked with one another in afirst local communication network 18, for example an Intranet or LAN. Ina second local communication network 18 separate from the first, forexample an Intranet or LAN, a plurality of OPC servers, of which onlyone OPC server 21 has been designated for reasons of clarity, arenetworked with one another.

[0037] In order to make OPC communication possible between the two localcommunication networks 18, 19 via the Internet 24, one computer 22functions as an HTTP client 25. All the OPC calls from the OPC client ofthe first local communication network 18 are sent to the computer 22 andfrom there, via communication via the Internet 24, are transported tothe HTTP server 17, located in the computer 23 in the second localcommunication network 19. In the view of the OPC client, therefore, thecomputer 22 behaves like an OPC server 25 and, at the same time, is anHTTP client 25 for the communication via the Internet 24. The HTTPserver 17 passes on the received OPC calls to the associated OPC serversof the second local communication network 19. Thus, in the view of theOPC server, the computer 23 behaves like an OPC client 17 and, at thesame time, is an HTTP server 17 for the communication via the Internet24.

[0038] This communication via the Internet 24 is carried out by means ofthe bidirectional transmitting and receiving connection described inFIG. 2, capable of initiation from both sides and mutuallychronologically independent, between the HTTP client 25 or OPC server 25and the HTTP server 17 or the OPC client 17. Of course, the HTTP client25 or OPC server 25 and the HTTP server 17 or OPC client 17 in each casecarry out the necessary conversions already described in relation toFIG. 2 into the necessary data formats.

[0039] In summary, the invention thus relates to a system and a methodfor transmitting OPC data via data networks, in particular the Internet,in particular OPC data for operating and observing an automation system5. For a bidirectional useful data connection even behind firewalls viathe Internet in both directions, even from an OPC client 1 which is notvisible as a server in the Internet, a method and a system are proposedin which, from a first data processing device of an OPC client 1, inparticular from an operating and observation system 1, via a dataconnection 6, 7, 8, in particular an Internet connection, a firstconnection request to establish a first transmission channel 6 a, 7 a, 8a is sent to an O&O or OPC server 4 of an automation system 5. Aresponse to this is made via a second transmission channel 6 b, 7 b, 8b. A chronologically unlimited useful duration of the data connection 6,7, 8 is ensured in that, in order to maintain the data connection 6, 7,8, for example even when there is no useful OPC data present, dummy datais transmitted or, that information is sent to the OPC client 1 whichinforms the client 1 that transmission of useful OPC data is stillintended. This results in a permanently open data connection 6, 7, 8 viawhich the O&O or OPC server 4, and therefore the automation system 5, atany time and independently of actions of the OPC client 1, can send dataasynchronously to the OPC client 1 and therefore to the O&O system 1.

1. A method for transmitting OPC data via data networks, in particularthe Internet (10), in which a first connection request for establishingat least one first transmission channel (6 a, 7 a, 8 a) is sent from anOPC client (1) via a data connection (6, 7, 8) to at least one OPCserver (4), at least one data connection (6, 7, 8) being permanentlyopen, which is provided for sending, at any desired time andindependently of the actions of the OPC client (1), OPC data from atleast one OPC server (4) to the OPC client (1) via at least one datanetwork.
 2. The method as claimed in claim 1, characterized in that inorder to maintain a data connection (6, 7, 8) permanently between atleast one OPC server (4) and at least one OPC client (1), dummy data istransmitted even when there is no useful OPC data present.
 3. The methodas claimed in claim 1 or 2, characterized in that the dummy data is sentfrom the OPC server (4) to the OPC client (1).
 4. The method as claimedin one of the preceding claims, characterized in that when useful OPCdata is not present, dummy data is transmitted from the OPC server (4)to the OPC client (1) every 25-35 seconds.
 5. The method as claimed inone of the preceding claims, characterized in that in order to maintaina data connection (6, 7, 8) permanently, the OPC server (4) sends to theOPC client (1) information which informs the OPC client (1) that atransmission of data is intended.
 6. The method as claimed in one of thepreceding claims, characterized in that in order to maintain a dataconnection (6, 7, 8) permanently, via which quantities of data up to adefined size are transmitted from the OPC server (4) to the OPC client(1), a requirement for a new connection request is sent from the OPCserver (4) to the OPC client (1) before the defined quantity of data isreached, and then a new connection request for establishing at least onenew transmission channel is sent from the OPC client (1) to the OPCserver (4).
 7. The method as claimed in one of the preceding claims,characterized in that the quantity of data to be transmitted via onetransmission channel have a size of 15-25 MB.
 8. The method as claimedin one of the preceding claims, characterized in that a transportprotocol, in particular an Internet transport protocol, is provided tocontrol the data transmission.
 9. The method as claimed in one of thepreceding claims, characterized in that the transport protocol providedis a Hypertext Transport Protocol.
 10. The method as claimed in one ofthe preceding claims, characterized in that the method is provided foroperating and observing an automation system (5) via at least one datanetwork, in particular via the Internet (10).
 11. The method as claimedin one of the preceding claims, characterized in that before being sentvia the Internet by a transmitting station, the OPC data is convertedinto an Internet-compatible data format and sent via the Internet to areceiving station and, following the transmission, the data received inthe Internet-compatible data format is converted into OPC data again bythe receiving station.
 12. The method as claimed in one of the precedingclaims, characterized in that the OPC client (1) is not visible in theInternet (10).
 13. The method as claimed in one of claims 1 to 13,characterized in that the OPC client (1) has not installed an InternetInformation Server.
 14. The method as claimed in one of the precedingclaims, characterized in that the operating and observation sytem (1) ofthe OPC client (1) initiates the provision of at least one transmissionchannel (6 a, 7 a, 8 a) as a distributed object, in particular as a DCOMobject, and in that the establishment of the connection to theautomation system (5) is carried out via a DCOM server (4) and/or an OPCserver (4).
 15. A system for transmitting OPC data via data networks, inparticular the Internet (10), comprising at least one data processingdevice (1) that can be coupled to a data network and belongs to an OPCclient (1), the first data processing device (1) being provided toestablish at least one data connection (6, 7, 8) in the form of a firsttransmission channel (6 a, 7 a, 8 a) to at least one OPC server (4), atleast one data connection (6, 7, 8) being permanently open, which isprovided for sending, at any desired time and independently of theactions of the OPC client (1), OPC data from at least one OPC server (4)to the OPC client (1) via at least one data network.
 16. The system asclaimed in claim 15, characterized in that the system to maintain a dataconnection (6, 7, 8) permanently between at least one OPC server (4) andat least one OPC client (1) has means of transmitting dummy data evenwhen there is no useful OPC data present.
 17. The system as claimed ineither of claims 15 and 16, characterized in that the system formaintaining a data connection (6, 7, 8) permanently has means forsending information from the OPC server (4) to the OPC client (1), whichinform the OPC client (1) that a transmission of data is intended. 18.The system as claimed in one of claims 15 to 17, characterized in thatthe system to maintain a data connection (6, 7, 8) permanently, viawhich the quantitative data up to a defined size are transmitted fromthe OPC server (4) to the OPC client (1), has means which, before thedefined quantity of data is reached, send a requirement for a newconnection request from the OPC server (4) to the OPC client (1) andcause the OPC client (1) to send a new connection request to establishat least one new transmission channel to the OPC server (4).
 19. Thesystem as claimed in one of claims 15 to 18, characterized in that thesystem uses a transport protocol, in particular an Internet transportprotocol, as means of controlling the data transmission.
 20. The systemas claimed in one of claims 15 to 19, characterized in that the systemuses a Hypertext Transport Protocol as the transport protocol as a meansfor controlling the data transmission.
 21. The system as claimed in oneof claims 15 to 20, characterized in that the system is provided foroperating and observing an automation system (5) via at least one datanetwork, in particular via the Internet.
 22. The system as claimed inone of claims 15 to 21, characterized in that the system has means whichconvert OPC data, before it is sent via the Internet from a transmittingstation into an Internet-compatible data format and send said data to areceiving station via the Internet and, after the transmission, the datareceived in the Internet-compatible data format is converted into OPCdata again by the receiving station.
 23. The system as claimed in claim22, characterized in that the transmitting station is an OPC client (1)and/or an OPC server (4).
 24. The method as claimed in claim 22characterized in that the receiving station is an OPC client (1) and/oran OPC server (4).
 25. The system as claimed in one of claims 15 to 24,characterized in that the operating and observation system (1) of theOPC client (1) initiates the provision of at least one transmissionchannel (6 a, 7 a, 8 a) as a distributed object, in particular as a DCOMobject, and in that the connection to the automation system (5) isestablished via a DCOM server (4) and/or an OPC server (4).